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Low voltage to fuel pump

I have a 97 ford ranger with a 4.0 L. Getting only 6.2 volts to new pump. Replaced relay but I was told to check for bad fuse. There is no listing in owners or repair books. Does anyone know where this lost fuse might be found? I will also use any other tips that anyone might have to offer.

Make sure the place you using for the ground of your meter test lead is a proper ground test point.

What voltage does your manual tell you to expect to see at the point you are testing.

Are you observing the proper ignition key position when making yor measurement.

Follow upstream on the circut and determine where you do have the proper voltage.

Fuses are either open or closed,I suppose corrosion at the fuse could cause a partial voltage drop but I suspect a connection or ground is where you are loosing voltage.

The fuse is called: Fuel System/Anti-theft Maxi-fuse. It’s under the hood, in the fuse/relay box.
You are getting voltage, so, the fuse is ok. You should have 12 volts at the dark green/yellow wire at the fuel pump relay. The inertial fuel shutoff switch is between the relay and the fuel pump. The pink/black wire from the inertial switch to the fuel pump should have 12 volts. You can measure the voltage, on the pink/black wire, at the fuel pump. Here’s the wiring diagram. Click on fig. 32.
If there is a lower voltage (12 volts) after the inertial switch, it’s likely caused by the inertial switch, or, the electrical connector(s).

Suppose to be 12 volts. I guess I must have been real tired when bringing up the bad fuse. It has to be open or closed. Thanks for the reminder.

hellokit, did all the above mentioned checks. All good except for the pink/blk wires. Reading 6.8 volts. Checked the fuel shut off switch to make sure it was not tripped. It was ok. Ran another ground wire from the inertial switch,at fuel tank , to ground. Still only 6.8 volts. What next???

It would appear that somewhere between the fuse and the fuel pump is a poor connection.

Whats the voltage at the inertia switch? You should see 12 volts for about 2 seconds when you turn the key & then it times out

As oldschool mentioned be sure you have your vom properly grounded.

Theres probably a ground screw at the bottom of the dash that you can use.

The only items in this circuit are the fuse, the relay, the inertia switch, and the pump. Low voltage to the pump can only be from a low voltage at the source or a resistance in the circuit (“dropping” voltage). The only possible places for a resistance are connections (which could be anywhere including a corroded fusebox terminal), relay contacts corroded (but you’ve already changed that) or internal to the inertial switch.

This is one of those jobs where you just have to start at the pump and work backwards up the circuit until you find where the balance of the voltage is being dropped. I’m not really saying anything different from others, I just thought perhaps a different perspective would help.

Thanks for all the help. Turns out it was the computer.

You’re only going to see 12+ volts at the pump just like at the inertia switch for two seconds after the ignition’s turn to run and then it’ll drop back down and it won’t go back up again to 12+ until the motors turning 400+ RPMs . The two second 12Volt hit is just to prime the pump.

Mike , you just replied to an 11 year old thread . And JR posted in Oct. 2008 that the problem was solved with a new computer .

Ok thanks, I’m going to have to check them post dates from now on :crazy_face: